AdminSite.get_model_admin raises AttributeError when `to` model of a ForeignKey is defined as a string

[Parth Paradkar]

I have a foreign key on one of my models defined as-

slack_alert = models.ForeignKey(
        "falcon.SlackAlert",
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name="tickets",
    )

When I do not include the falcon app in INSTALLED_APPS, the admin site raises an error (which is expected). However, while handling the expected KeyError, it throws an AttributeError. I am guessing this is since it expects a Model instance.

Traceback-

Traceback (most recent call last):
  File "/Users/parthparadkar/projects/lighthouse/venv/lib/python3.11/site-packages/django/contrib/admin/sites.py", line 170, in get_model_admin
    return self._registry[model]
           ~~~~~~~~~~~~~~^^^^^^^
KeyError: 'falcon.SlackAlert'

During handling of the above exception, another exception occurred:

  File "/Users/parthparadkar/projects/lighthouse/venv/lib/python3.11/site-packages/django/contrib/admin/checks.py", line 209, in _check_autocomplete_fields
    [
  File "/Users/parthparadkar/projects/lighthouse/venv/lib/python3.11/site-packages/django/contrib/admin/checks.py", line 210, in <listcomp>
    self._check_autocomplete_fields_item(
  File "/Users/parthparadkar/projects/lighthouse/venv/lib/python3.11/site-packages/django/contrib/admin/checks.py", line 239, in _check_autocomplete_fields_item
    related_admin = obj.admin_site.get_model_admin(field.remote_field.model)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/parthparadkar/projects/lighthouse/venv/lib/python3.11/site-packages/django/contrib/admin/sites.py", line 172, in get_model_admin
    raise NotRegistered(f"The model {model.__name__} is not registered.")
                                     ^^^^^^^^^^^^^^
AttributeError: 'str' object has no attribute '__name__'. Did you mean: '__ne__'?

I think this can be fixed by checking with isinstance before raising NotRegistered?

 except KeyError:
    if isinstance(model, str):
        raise NotRegistered(f"The model {model} is not registered.")
    else:
        raise NotRegistered(f"The model {model.__name__} is not registered.")

[Jacob Walls]

Thanks. I'd suggest {model!r} instead of {model} but otherwise LGTM.

[Jacob Walls]

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